Ringing circuit for carrier frequency communication systems



June 30,1942. 2,288,252

RINGING CIRCUIT FOR CARRIER FREQUENCY COMMUNICA T-ION SYSTEMS Filed Nov. 27, 1940 2% 2 All" Patented June 30, 1942 SAT T e r i e Herbert Nitz, Berlin, Germany, assigner to C. Lorenz Aktiengesellschaft, Berlin-Tempelhof,

Germany, a company Application November 27, 1940, Serial No. 367,417 in Germany December 8, 1939 1 Claim.

The call translator interposed between the trunk line terminal circuit and the trunk position in order to serve for the customary voice frequency ringing, must in the case of carrier frequency transmission of intelligence convert the voice frequency call, arriving in carrier frequency fashion, into the local ringing frequency, as 20 cycles per second, for instance.

According to the present invention it is proposed that a highly resistive demodulator be connected in advance of the call translator and in the line side input circuit thereof.

The call translator is not'aiiected thereby in its operation and the outgoing voice frequency ringing passes over the low-pass filter of the carrier frequency terminal arrangement to the outgoing trunk line.

The accompanying drawing shows a diagrammatic representation of one embodiment of the invention, namely, a call translator for the carrier frequency terminal circuit.

The conductor pair indicated a, b on the lefthand side of the drawing extends to the carrier frequency terminal circuit and the other conductor pair a, b on the right-hand side of the drawing extends to the trunk position. RU is a call translator arranged to convert a 500-cycleringing signal interrupted at 20 cycles per second and arriving from the carrier frequency terminal circuit into 20-cycle current, and to convert a 20-cycle ringing signal arriving from the trunk position into a 500-cycle ringing current interrupted at 20 cycles per second. D is an additional demodulator inserted between the line a, band the call translator RU. The tuned call receiving relays are indicated R and W and their contacts are indicated 1 and w respectively.

In operation, a 500 cycle ringing signal interrupted at 20 cycles and modulated by a carrier wave arriving from the carrier frequency terminal circuit, is demodulated in the demodulator D and the resultant 500 cycle current interrupted at 20 cycles is applied to the call translator EU and translated into a 20 cycle current which operates the tuned relay R. The relay R at its contacts 1 applies a local source of ZO-cycle ringing current to the conductor pair extending to the trunk position.

In the opposite direction, a 20-cycle ringing signal from the trunk position operates the tuned relay W which at its contacts w applies a 500- cycle ringing current interrupted at 20 cycles to the conductor pair which extends to the carrier frequency terminal circuit. Condensers C are blocking condensers which prevent the incoming ZO-cycle ringing current from flowing directly to the outgoing line.

Since the demodulator D is connected directly to the conductors extending from the carrier frequency terminal circuit to the trunk position it is necessary that it should present at its input a high ohmic resistance both to speech modulated carrier waves proceeding in the direction from the carrier frequency terminal circuit to the trunk position and to low frequency speech currents proceeding in the opposite direction, in order that the call translator shall not cause undesirable attenuation of the speech signal waves in either direction of transmission.

What is claimed is:

In a carrier frequency terminal circuit, a line for receiving a carrier current modulated by a voice frequency ringing current, a line extending to a trunk position, a call translator for responding to said voice frequency ringing current and for controlling the application of a source of local ringing current to said last-mentioned line, an input circuit for said call translator, a demodulator having a high ohmic input resistance connected in the input circuit of said call translator, and a direct connection from the input circuit of said demodulator to said first-mentioned line.

HERBERT NITZ. 

